Apparatus for making a nonwoven web



July 30, 1968 T. E. C. KNEE APPARATUS FOR'MAKING A NoNwovN WEB Filed may51, 196e -nal-n Univ/UHU `mvENToR $24 .29 Tem-:Nee 5.o. KNEE UnitedStates Patent O 3,394,435 APPARATUS FOR MAKING A NONWOVEN WEB Terence E.C. Knee, Wilmington, Del., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed May 31, 1966, Ser. No. 554,099 2 Claims.(Cl. 19-156.3)

This invention relates to an apparatus for depositing fibrous materialsbeing transported in a moving fluid medium, such as air, onto a movingreceiver as a non- Woven web, and in particular to an apparatus whereinthe fibrous materials, after deposition, are firmly held to the receiverso that they do not shift their position under the influence of aircurrents.

In the adaptation of the recently developed process for the preparationof continuous-filament webs, described in British Patent 932,482, toeconomical commercial production of wide nonwoven webs, it is necessary,in order to obtain the desired productivity, to use a plurality ofspinnerets or other filament-producing devices and collect the outputsfrom these spinnerets as a nonwoven web of the desired width. Thespinnerets may be located across the width of the web to be produced,and positioned so that the filaments, after having been molecularlyoriented by drawing and electrostatically charged, can be forwardedtoward the laydown zone and deposited in overlapping ribbons to form thenonwoven web.

The electrostatic charge is applied to the filaments to cause them toseparate when the tension on them is released and thus permit thecollection of uniform, nonblotchy nonwoven webs. Jet devices, which usea highvelocity stream of air flowing cocurrently with the lamentsthrough the device, are preferred for forwarding the electrostatioallycharged filaments because the tension which the jet devices apply to thefilaments is rapidly released as the filaments exit from the jet deviceand therefore the filaments are free to separate due to the appliedelectrostatic charge. When multiple jet devices are used, however, theair streams exiting from the jet devices and the electrostatic charge onthe filaments cause interference between the filaments exiting fromadjacent jet devices and prevents them from being combined uniformlyinto a non-directional web on the weblaydown receiver. It has been foundthat this interference between adjacent jet devices can be overcome bywithdrawal of at least 5 times the amount of lair supplied to the jetdevices through the foraminous receiver into a suction or plenum chamberlocated below'the weblaydown zone.

The withdrawal of this large quantity of air, however, increases the airmovement across the web yand this causes the filaments to blow up, andthe nonwoven web to curl, overlap and become non-uniform in the regionwhere the freshly-deposited web leaves the suction area at thedownstream side of the suction chamber.

In the instant method the aforementioned difficulties are overcome. Theair stream exiting from the jet device and containing the bundle isdirected toward a stationary depositing zone over the moving foraminousweblaydown receiver while suction is applied to the underside of thereceiver in the :area beneath the depositing zone. Substantially all theair of the stream exiting from the jet passes through the foraminousreceiver while the filaments contained inthe stream are retained on thereceiver. As the filaments, now in the form of a deposited web, arecarried downstream from the area of deposition by the moving receiver,suction is applied to the underside of the receiver in a second areathat is contiguous to the first area beneath the depositing Zone. Thesuction 3,394,435 Patented July 30, 1968 ICC applied is greatest in theregion immediately adjacent the suction area under the depositing zoneand diminishes or decreases in intensity in the downstream direction.Thus a decreasing air flow gradient exits across the receiver from theregion contiguous to the suction area under the depositing zone to thedownstream region of said second suction area. The air flow is reducedto zero where the web leaves the second suction area.

The apparatus of this invention eliminates this shifting of thefilaments after laydown and makes possible the high-speed deposition offilaments onto a moving foraminous rece-iver as a uniform nonwoven web.The apparatus comprises, in combination with a .primary suction chamberlocated below a web-laydown receiver for initially attracting landhold-ing filaments to the receiver, a secondary suction chamber locatedbelow the weblaydown receiver and contiguous with the downstream side ofthe primary suction chamber, the secondary suction chamber comprisingmeans for providing a decreasing air flow gradient from the side of thesecondary suction chamber contiguous to the primary suction chamber tothe downstream side where the web leaves the suction zone of thesecondary suction chamber.

The invention will be further understood by reference to the drawings inwhich FIGURE l is an isometric view showing in part an apparatus forproducing la wide nonwoven web and outlining the placement of theprimary and secondary suction chambers; and

FIGURE 2 is an enlarged cross-sectional view taken along line 2-2 ofFIGURE 1 showing preferred embodiments of primary and secondary suctionchambers.

The essential parts of an apparatus suitable for producing wide,continuous-filament nonwoven webs are shown in FIGURE 1. For clarityonly one filamentspinning position including the means forelectrostatically charging and drawing the filaments and only threefilament-forwarding jet devices are shown. The addition-al positions:and jet devices are identical to those shown and are provided in thenumber required to produce the desired width of nonwoven web byoverlapping the adjacent ribbons of nonwoven web laid down on the movingreceiver. In FIGURE 1, filaments 10 are extruded from spinneret 11 andcombined into a bundle on snub bar 12. Snub bar 12 may be cylindrical asshown or may have a convex or concave surface to cause divergence orconvergence of the filament bundle, respectively. Alternatively, a combdevice may be used in place of the snub bar 12 to regulate the width ofthe filament bundle and maintain it in the desired alignment with thedraw rolls and jet device downstream there-l from. The filaments arethen electrostatically charged by means of corona-discharge devicescomprising target bars 13 and charge heads 14. The filament bundle ispassed into light contact with slowly rotating target bars 13 which areposittioned adjacent char-ge heads 14 which have needle electrodes. Acorona discharge is generated by applying a high electric potential tothe electrodes and grounding the target bars.

The charged filaments pass over draw rolls 15 and then into stationaryslot jets 16 which strip the filaments from the last draw roll andforward them toward the web-laydown receiver 17. The slot jets areprovided with air through inlets 18. The jet devices are equipped withdiffuser sections 19 to spread the filament bundles and provideelongated areas of deposition which are readily blended by overlappingabout 67% into a wide, uniform nonwoven web.

The filaments are collected on moving foraminous receiver 17 above theprimary suction chamber 20 as web 21. Air is withdrawn through thereceiver into the suction chamber and then through exhaust duct 22 whichis attached to a suction-blower system not shown. The air withdrawnthrough the receiver into the primary suction chamber serves to overcomethe aerodynamic and electrostatic interference betweenlaterally-adjacent jet devices. ln order to utilize electrostaticattraction as well as aerodynamic forces to attract and hold the chargedfilaments to the receiver, the receiver may be a grounded metal screenor alternatively, if a fabric belt is used, the surfaces of the primaryand secondary suction chambers which contact the belt are grounded and agrounded metal plate is positioned below the belt in the regiondownstream from the secondary suction chamber.

The secondary suction chamber 23 is positioned adjacent to thedownstream side 24 of primary suction chamber and is provided withmeans, not shown in FIGURE l, to provide a decreasing air-flow gradientin the direction of arrow 25. The air withdrawn t-hrough the receiverinto the secondary suction chamber is controlled and graduated in such away that the effect holding the filaments to the receiver decreasesgradually from a high level at the primary suction chamber to lowerlevels over the secondary suction chamber, and to virtually zero as thenonwoven web leaves the suction zone of the secondary suction chamber.This gradient is essential and satisfactory results cannot be obtainedmerely by applying a high vacuum to both suction chambers. Ordinarilythe air velocity differential in going from suction to no suction, i.e.the point where the web leaves the secondary suction zone should notexceed 50 Ift./ min. In going from first suction zone to the secondarysuction zone the air velocity differential should preferably not exceedabout 150 ft./min. The stepwise reduction in air velocity shouldpreferably not exceed about 30 ft./min. per three inches of receiverwidth.

In FIGURE 2, the primary suction chamber 20 holds the filaments to thereceiver from the time they touch until they are clear of the stream ofair exiting from the jet devices. Virtually all of the air from the jetdevices enters the primary suction chamber. In a preferred embodiment ofthe primary suction chamber, the chamber comprises an orifice plate 26,a perforated cover plate 27, and a multiplicity of independentfluid-distribution cells 28 forming a honeycomb structure between theorifice plate and cover plate. The cells are open at both ends, thelower end being in contact with the orifice plate and positioned over asingle hole in the orifice plate, and the upper end being in contactwith the cover plate. The cover plate may have an open area below eachjet device conforming with and slightly larger than the pattern of thejet air striking the laydown receiver above the primary suction chamber.These open areas may consist of perforated portions in an otherwisesolid cover plate or may be present in a mask plate positioned over theperforated cover plate.

The embodiment of secondary suction chamber shown in FIGURE 2 consistsof an outer shell 29 which is solid except for exhaust duct 30, which isattached to an auxiliary suction-blower system not shown, and the topsurface. The top consists of three elements plus a support frame. Auniformly perforated or foraminous plate 31, which is relatively open toair flow, is located directly below and in contact wit-h web-laydownreceiver 17. Below plate 31 is mask 32 made of layers of a woven ornonwoven fabric, with increasing numbers of layers toward the exit edgeof the secondary suction chamber, thereby providing a gradient ofincreasing resistance to airflow. Of course, a single layer ofincreasing thickness would be equally suitable. Below mask 32 is agrating 33 which supports mask 32 and offers little restriction to airow. A series of bea-ms 34, which have no significant effect on the airow, support the grating above the bottom of the secondary suctionchamber. Since plate 31 is normally a light-weight material which issupported only by mask 32 in the region between the side walls of thesuction chamber, it is desirable to have beams 34 adjustable so that theplate can be maintained in a level position across its entire width.

While the above-described embodiment of the secondary suction chamber ispreferred because of excellent performance, simplicity and low cost,other methods for obtaining a gradient lof resistance to air flow canalso be used. For example, the open area in the perforated plate 31 maybe gradually decreased by decreasing the number and/ or size of theperforations in the direction of travel of the receiver. Alternatively,a honeycomb structure of the type described above in the primary suctionchamber may be used, with the holes in orifice plate lbeing decreased insize in the direction of travel of the receiver.

eparate primary and secondary suction chambers with separatesuction-blower systems are preferred because they provide greatversatility to the laydown operation and precise control over theair-ows. These factors are of considerable importance because thepreparation of various types of non-wo-ven products can require the useof different process conditions in the spinning and subsequenttreatments of the filaments. These different process conditions mayrequire different velocities of jet air. For each jet air velocity,there are optimum levels of air Withdrawal for both the pri-mary andsecondary suction chambers and these optimum levels can be readilyobtained With separate chambers. If, however, only a single type ofnonwoven web is to be produced, it is possible to use a single suctionchamber with two portions corresponding to and functioning in accordwith the above-described primary and secondary suction chambers, andwith both of these portions being connected to the same suctionblowersystem. It is intended that this type of suction chamber come within thescope of the present invention.

What is claimed is:

1. Apparatus comprising a movable foraminous weblaydown receiver onwhich to form a nonwoven web, a plurality of means -for discharging astream of air containing a plurality of fila-ments onto one face of saidreceiver, a primary suction-chamber located at the opnosite face of saidreceiver and opposite the said discharging means, for withdrawing airthat is directed at the web-laydown receiver by said discharge means andthat passes through said web-laydown receiver, and a secondarysuction-box located below the web-laydown receiver and contiguous withthe downstream side of the primary suction-chamber, the secondarysuction-chamber having means for successively increasing resistance toow from the side of the secondary suction-chamber contiguous to theprimary suction-chamber to the downstream side where the web leaves thesuction zone of the secondary suction chamber.

2. The apparatus of claim 1 wherein the means providing an increasingresistance to air flow comprises layers of fabric increasing in numbertoward the exit edge of the secondary suction chamber.

References Cited UNITED STATES PATENTS 2,859,506 ll/l958 Slayter 28ll2,940,135 6/1960 Heritage 19-l56.3 2,993,239 7/1961 Heritage lO-l56.33,114,939 12/1963 Labino 19-l56.3

MERVIN STEIN, Primary Examiner'.

I. C. WADDEY, Assistant Examiner.

1. APPARATUS COMPRISING A MOVABLE FORAMINOUS WEBLAYDOWN RECEIVER ONWHICH TO FORM A NONWOVEN WEB, A PLURALITY OF MEANS FOR DISCHARGING ASTREAM OF AIR CONTAINING A PLURALITY OF FILAMENTS ONTO ONE FACE OF SAIDRECEIVER, A PRIMARY SUCTION-CHAMBER LOCATED AT THE OPPOSITE FACE OF SAIDRECEIVER AND OPPOSITE THE SAID DISCHARGING MEANS, FOR WITHDRAWING AIRTHAT IS DIRECTED AT THE WEB-LAYDOWN RECEIVER BY SAID DISCHARGE MEANS ANDTHAT PASSES THROUGH SAID WEB-LAYDOWN RECEIVER, AND A SECONDARYSUCTION-BOX LOCATED BELOW THE WEB-LAYDOWN RECEIVER AND CONTIGUOUS WITHTHE DOWNSTREAM SIDE OF THE PRIMARY SUCTION-CHAMBER, THE SECONDARYSUCTION-CHAMBER HAVING MEANS FOR SUCCESSIVELY INCREASING RESISTANCE TOFLOW FROM THE SIDE OF THE SECONDARY SUCTION-CHAMBER CONTIGUOUS TO THEPRIMARY SUCTION-CHAMBER TO THE DOWNSTREAM SIDE WHERE THE WEB LEAVES THESUCTION ZONE OF THE SECONDARY SUCTION CHAMBER.